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Revision to Capability Codes Registration Procedures
RFC 8810

Document Type RFC - Proposed Standard (August 2020)
Updates RFC 5492
Author John Scudder
Last updated 2020-08-17
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
IESG Responsible AD Alvaro Retana
Send notices to (None)
RFC 8810

Internet Engineering Task Force (IETF)                        J. Scudder
Request for Comments: 8810                              Juniper Networks
Updates: 5492                                                August 2020
Category: Standards Track                                               
ISSN: 2070-1721

          Revision to Capability Codes Registration Procedures


   This document updates RFC 5492 by making a change to the registration
   procedures for BGP Capability Codes.  Specifically, the range
   formerly designated "Private Use" is divided into three new ranges:
   "First Come First Served", "Experimental Use", and "Reserved".

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Discussion
   3.  IANA Considerations
   4.  Security Considerations
   5.  References
     5.1.  Normative References
     5.2.  Informative References
   Author's Address

1.  Introduction

   The Border Gateway Protocol uses a mechanism called "Capability
   Advertisement" [RFC5492] to enable BGP peers to tell one another
   about their optional protocol extensions.  These so-called
   "Capabilities" are signaled using code points called "Capability

   [RFC5492] designates the range of Capability Codes 128-255 as
   "Private Use".  Subsequent experience has shown this to be not only
   useless, but actively confusing to implementors.

   Accordingly, this document revises the registration procedures for
   the range 128-255, as follows, using the terminology defined in

   128-238:  First Come First Served
   239-254:  Experimental Use
   255:      Reserved

   The procedures for the ranges 1-63 and 64-127 are unchanged,
   remaining "IETF Review" and "First Come First Served", respectively.
   The full range for "First Come First Served" is now 64-238.

2.  Discussion

   The reason for providing an "Experimental Use" range is to preserve a
   range for use during early development.  Although there are few
   practical differences between "Experimental Use" and "Private Use",
   the change both makes it clear that code points from this space
   should not be used long term or in shipping products and reduces the
   consumption of the scarce Capability Codes space expended for this
   purpose.  Once classified as "Experimental Use", it should be
   considered difficult to reclassify the space for some other purpose
   in the future.

   The reason for reserving the maximum value is that it may be useful
   in the future if extension of the number space is needed.

   Since the range 128-255 was formerly designated "Private Use",
   implementors may have chosen to use code points within that range
   prior to publication of this document.  For this reason, a survey was
   conducted beginning August 14, 2015 (version 01 of the individual
   draft [SCUDDER]) to find any such uses.  A number were contributed
   and were used to seed Table 2.  Of course, there can be no guarantee
   that all uses were discovered; however, the likelihood seems high
   that remaining uses, if any, genuinely do fall under the intended use
   of "Private Use" and are restricted to some special deployment and
   are not in wide use.  Furthermore, any remaining uses would be no
   worse than any other code point collision, such as occasionally
   occurs with code point "squatting", and could be dealt with in the
   same manner.

3.  IANA Considerations

   IANA has revised the "Capability Codes" registry as follows.

   Reference: [RFC5492] and this document.

   Note: The IETF will be the Change Controller for all future

   Registration procedures:

                   |  Range  | Registration Procedures |
                   |   1-63  | IETF Review             |
                   |  64-238 | First Come First Served |
                   | 239-254 | Experimental Use        |

                                  Table 1

   IANA has made the following new allocations within the "Capability
   Codes" registry:

      | Value | Description                | Reference | Change     |
      |       |                            |           | Controller |
      |  128  | Prestandard Route Refresh  | RFC 8810  | IETF       |
      |       | (deprecated)               |           |            |
      |  129  | Prestandard Outbound Route | RFC 8810  | IETF       |
      |       | Filtering (deprecated),    |           |            |
      |       | prestandard Routing Policy |           |            |
      |       | Distribution (deprecated)  |           |            |
      |  130  | Prestandard Outbound Route | RFC 8810  | IETF       |
      |       | Filtering (deprecated)     |           |            |
      |  131  | Prestandard Multisession   | RFC 8810  | IETF       |
      |       | (deprecated)               |           |            |
      |  184  | Prestandard FQDN           | RFC 8810  | IETF       |
      |       | (deprecated)               |           |            |
      |  185  | Prestandard OPERATIONAL    | RFC 8810  | IETF       |
      |       | message (deprecated)       |           |            |
      |  255  | Reserved                   | RFC 8810  | IETF       |

                                  Table 2

4.  Security Considerations

   This revision to registration procedures does not change the
   underlying security issues inherent in the existing [RFC5492] and

5.  References

5.1.  Normative References

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,

5.2.  Informative References

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,

   [SCUDDER]  Scudder, J., "Revision to Capability Codes Registration
              Procedures", Work in Progress, Internet-Draft, draft-
              scudder-idr-capabilities-registry-change-01, 14 August
              2015, <


   Thanks to Alia Atlas, Bruno Decraene, Martin Djernaes, Jie Dong, Jeff
   Haas, Sue Hares, Acee Lindem, Thomas Mangin, and Tom Petch for their
   reviews and comments.

Author's Address

   John Scudder
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA 94089
   United States of America